Google has announced its official short url g.co
Any link of g.co will you take you to a Google product or service. So, you are absolutely safe when clicking any link of g.co
The site with Google logo says following:
You’ve arrived at this page because you typed or linked to “g.co”, Google’s official URL shortcut just for Google websites.
Whenever you see a short “g.co” link, you can trust that it will always take you to a Google product or service.
We also have a public URL shortener at goo.gl. You can use this to shorten up URLs across the web.
Twitter also has a official short url t.co used to short urls / links posted on Twitter.com
Google also has a public short url service at goo.gl